There are always requirements for improvements in the art of drying paper web materials of all grades. As an example, the manufacture of container board is open to changes and improvements due to amendments to the United States shipping industry Rule 41. For over seventy years the container industry specifications for boxes have been governed by the parameters of maximum weight of the contents relative to given container dimensions, combined with bursting strength, puncture strength and basic weight of linerboard and corrugated medium. In view of the amended Rule 41, the relationship between the maximum weight of the contents versus the outside dimension of the container is maintained but "edge crush strength" takes the place of other requirements.
The current procedures of stacking containerized goods can sometimes lead to the collapse of the lowermost containers with resulting damage to the contents therein. In order to determine acceptable stacking limitations, an edge crush test for the combined container board and a ring crush test for linerboard and the corrugated medium have been introduced.
Conventional methods of producing container board are inefficient when it comes to providing a product to meet the new requirements. Current manufacturing methods use too much fibre to manufacture a high performance container board that has the edge and strength requirements as specified in Rule 41.
One example of prior practice is shown in U.S. Pat. No. 3,447,247 Daane of Jun. 3rd, 1969. In this patent, the process utilizes impingement air jets to penetrate the paper web and push the water out of the web. Reference is made in the patent towards the production of tissue paper, specific mention being made of a wet permeable web. The Daane process uses air jets and the air therefrom is caused to pass through the web by momentum. There is some suction but it is very localized opposite the impingement jet nozzles.
A further example of prior art is disclosed in British Patent 1,600,518 published Oct. 14, 1981. This specification discloses a web drying apparatus utilizing a suction box for applying vacuum to the underside of the web and Using air caps over the web for applying drying air to the upper surface thereof. However, mention is made of only 1 to 2 inches of H.sub.2 O and possibly up to 4 inches for the use of threading. However, there is no reference in the specification for the use of suction to restrain a paper web nor is there any disclosure of using such suction in the ranges specified in the present invention.
Another example of the known art is seen in U.S. Pat. No. 4,680,873 of Jul. 21, 1987 to Fellers et al. This patent discloses a method and apparatus to control or regulate the shrinkage and/or the stretching of a paper web transverse to it's travelling direction. At a point in the process where the paper web has a certain dry solids content, the paper is subjected to an outwardly directed force that acts in the edge portion of the web. The means applying the outwardly directed force direct streams of pressurized air against the edge portions to create frictional forces against the paper. The means may also utilize a combination of air streams and mechanical devices such as strip-like members located on each side of the web and to accompany the web over drying cylinders, the members being fixed to the cylinders by grooves therein. An example is found in "A New Method for Restrained Drying of Paper in the Cross Direction", I. Karlsson Eucepa 1990, page 286.
A further example of known art is U.S. Pat. No. 5,279,049 Jan. 18, 1994 Skaugin et al. This patent discloses a method and apparatus for the restrained drying of a paper web in the dryer section of a paper machine. In this patent, the method and apparatus described therein replaces heating means, namely steam cylinders with high temperature, high velocity air or superheated steam.
None of the references of the prior art referred to above discloses methods and apparatus for completely restraining a paper web in accordance with the method and apparatus of the present invention.
Further examples of the prior art are as follows:
U.K. Patent Application GB 2,001,370 A published Jan. 31, 1979; PA1 U.S. Pat. No. 4,036,684 issued Jul. 19, 1977; and PA1 PCT International Application WO93/23616 published Nov. 25, 1993.